Distances can be measured between a measuring device and an object without a physical contact between the device and the object by optical methods. In these methods, the object is illuminated by a light source of the device and the light back reflected from the object is then captured by a light detector of the device.
Distances can for example be determined by periodically modulating the light intensity which is emitted from the light source and by measuring the phase difference between the emitted light and the back reflected light arriving on the detector. However, due to the periodicity of the light intensity, this method results in an ambiguous distance measurement. Distances can be unambiguously determined by measuring the time of flight between the emission of a light pulse and the arrival of a back reflected light pulse on the detector.
Ambient light, for example sun-light, can interfere with the distance measurement and therefore result in a reduction of the precision for the distance measurement. Conventionally, a background measurement is carried out without illuminating the object with the light pulse. The background measurement leads to an irregular operation of the light source. The irregular operation is disadvantageous because it results in a reduction of the life time of the light source and in fluctuations of the parameters of the light pulses, in particular intensity, pulse width, rise times and/or fall times. These fluctuations cause a reduction of the precision for the distance measurement.